X-ray systems are used for medical, industrial and security inspection purposes because they can cost-effectively generate images of internal spaces not visible to the human eye. Materials exposed to X-ray radiation absorb the radiation differently and, therefore, attenuate an X-ray beam to varying degrees, resulting in a transmitted level of radiation that is characteristic of the material. The attenuated radiation can be used to generate a useful depiction of the contents of the irradiated object. The absorption of X-rays is measured by detectors after the beam has passed through the object and an image is produced of its contents and presented to an operator. An example of X-ray systems used in medical applications is for osteoporosis assessment and monitoring.
Osteoporosis is a disease of unknown cause which afflicts people, women more often than men, generally as they age. Osteoporosis, or porous bone, is a disease characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility and an increased susceptibility to fractures, especially of the hip, spine and wrist, although any bone can be affected. After a person reaches peak bone mass, the balance between bone loss and bone formation might start to change. In midlife, bone loss usually speeds up in both men and women. For most women, bone loss increases after menopause, when estrogen levels drop sharply. In fact, in the five to seven years after menopause, women can lose up to 20 percent or more of their bone density.
Bones are composed of both corticular (compact bone) and trabecular (connective strands) bone, where in most areas of trabecular bone, the trabecular mass is surrounded by a relatively thin layer of cortical bone, which may vary in thickness depending upon the individual. High-stress regions of bone tend to be more in cortical bone. Osteoporosis affects trabecular bone more than corticular bone, and is characterized by an absolute decrease in bone tissue mass. Although not common, Secondary Osteoporosis has been termed for bone loss conditions in which the underlying causes of bone loss are typically excessive steroid use, alcoholism, or a sedentary lifestyle.
Conventionally, osteoporosis is diagnosed by conducting a bone mineral density (BMD) test (also referred to as “bone mass measurement”) in areas of the bone rich in trabecular bone. A lower reading of bone mineral density implies a greater risk of having a fracture. A BMD test is conducted for multiple reasons such as, to detect low bone density before a person breaks a bone, to predict a person's chances of breaking a bone in future, to confirm a diagnosis of osteoporosis when a person has already broken a bone, to determine whether a person's bone density is increasing, decreasing or remaining stable, and to monitor a person's response to treatment.
BMD test results are provided as a number termed as T-score, which indicates a measure of a person's bone density being above or below normal. FIG. 1A is a pictorial representation 101 of T-scores. As illustrated in FIG. 1A a T-score between +1 and −1 indicates normal bone density, a T-score between −1 and −2.5 indicates low bone density or osteopenia, and a T-score of −2.5 or lower is indicative of osteoporosis. BMD test results also include a Z-score which is used to compare a person's bone density to a normal bone density of a person of the same age and body size. A Z-score above −1.5 is typically normal. Z-scores are used mainly in younger people and children for comparison of the BMD result to other patients of the same age, gender, body size, and ethnic background and typically not used for diagnosis of osteoporosis. Applicant has invented treatment methodologies related to the measurement and use of BMD tests, which are embodied in U.S. patent application Ser. No. 10/623,466, entitled “Integrated Protocol for Diagnosis, Treatment, and Prevention of Bone Mass Degradation”, filed on Jul. 18, 2003, and herein incorporated by reference.
Bone density testing can be performed on different bones of a human body, including hip, spine, wrist, finger or heel. There are two basic methods of measuring bone density, one method utilizes X-rays and other method utilizes ultrasound waves. In one method, dual energy X-rays are used to simultaneously obtain two distinct images that represent different X-ray energy spectrum. These two distinct images are then analyzed to separate soft tissue from bone and provide a bone density measurement. Examples of bone density test techniques include hip and spine dual energy x-ray absorptiometry (Central DXA), peripheral dual energy x-ray absorptiometry (pDXA), quantitative ultrasound (QUS), quantitative computed tomography (QCT), and peripheral quantitative computed tomography (pQCT).
While ultrasound methods for determining bone loss condition have been employed in the past, clinical results have shown that they are not adequately accurate. For example, U.S. Pat. No. 6,086,538, assigned to Osteometer Meditech, Inc. and herein incorporated by reference, describes “[a] method of evaluating the status of bone tissue comprising measuring a characteristic of ultrasound transmission through a selected bone at a number of locations using a movable ultrasound transducer which is scanned over a body part containing said bone tissue so as to make said measurements at locations within an area at a spacing between measurement locations of no more than 5 mm, deriving from said measurements information regarding the location of a selected internal anatomical feature of the selected bone, and evaluating said bone tissue status based on ultrasound measurements which reflect said bone tissue status made at a location spatially defined with reference to said internal anatomical feature of the selected bone.”
Another prior art method for whole body BMD measurement uses a fan beam X-ray apparatus. For example, U.S. Pat. No. 5,838,765, assigned to Hologic and herein incorporated by reference, describes “[a] whole body x-ray bone densitometry system comprising: a table extending parallel to a Y-axis of an XYZ coordinate system for supporting a patient at a patient position; an x-ray source for emitting a narrow angle fan beam of x-rays to irradiate at any one time a scan line which is transverse to the Y-axis and is substantially shorter than the width of a body cross-section of a typical adult patient occupying the patient position; an x-ray detector aligned with said source along a source-detector axis which is transverse to the Y-axis, for receiving x-rays from the source within the angle of said fan beam after passage thereof through the patient position, said detector comprising a number of detecting elements arranged along a direction transverse to the Y-axis and to the source-detector axis; a source-detector support on which the source and detector are mounted at opposite sides of the patient position; and a scanning mechanism moving the patient table and the source-detector support relative to each other parallel to the Y-axis to scan the patient position with said narrow angle fan beam in successive scans parallel to the Y-axis in which the source-detector axis is at different angles relative to the patient position as between different ones of said successive scans, but in each of said successive scans an origin of the fan beam in the source is at the same vertical distance from the patient table.” The accuracy of the method, however, depends on correct patient positioning which may be inconvenient to the patient and also requires successive scans, increasing the patient's radiation exposure.
Yet another prior art method employs a Quantitative Computed Tomography (QCT) X-ray scanning technique where a three dimensional image of the skeletal region is produced and a determination of BMD can be made. For example, U.S. Pat. No. 7,174,000, assigned to Siemens Aktiengesellschaft and herein incorporated by reference, describes “[a] method for measuring a three-dimensional density distribution in a bone, comprising the steps of: disposing a bone to be measured in a region of a rotational axis of a measurement arrangement having an x-ray source and a two-dimensional radiation detector, disposed substantially opposite said x-ray source, rotatable around said rotational axis; irradiating a volume, comprised of voxels, of said bone with x-rays from said x-ray source while rotating said measurement arrangement around said rotational axis through an angle between 180° and 300°, and detecting, with said radiation detector, x-rays attenuated by said bone at a plurality of rotational angles of said measurement arrangement; at each of said rotational angles, and for each voxel, electronically calculating a density value dependent on said attenuated x-rays; and from said density values, electronically calculating an image of said volume representing a density distribution in said bone in said volume.” QCT techniques, however, have challenges in performing repeat clinical measurements, have higher radiation dose per scan to the patient, require long patient positioning time, and are a relatively high cost apparatus.
The above-mentioned conventional Bone Density Measurement systems, including quantitative computed tomography (QCT), hip and spine dual energy x-ray absorptiometry (Central DXA), and peripheral quantitative computed tomography (pQCT), require multiple scans in different angular positions to gather image information necessary to determine bone density. This requires longer patient scan time, requires patients to maintain a still body position for a longer duration of time and exposes patients to higher radiation dose. Maintaining a still position for long durations of time becomes difficult for patients and leads to erroneous readings and repeat scans. In addition, prior art systems tend to be large, bulky, difficult to move, and require large amounts of power.
Thus, what is needed is a bone density measurement system that involves a shorter patient observation/scan time; minimizes X-ray exposure to the patient; minimizes movement of the patient during the test; minimizes the effect of patient motion by gathering dual energy X-ray (High Energy and Low Energy) information close in time to each other; is light weight and portable; can be operated remotely and wirelessly for reducing clutter around the scanning apparatus; and supports a multilingual apparatus interface support, so that the system can be easily operated in various countries.
In addition, there is a need for a BDM system that is compatible with Digital Imaging and Communications in Medicine (DICOM) standards to allow for secure distribution and viewing of patient records.
Thus, there is a need for being able to accurately and reliably measure a patient's bone density and to correlate the results of similar tests on a large number of men and women of different ages so as to gain information on whether the patient is at increased risk of fracture.
There is also a need for being able to accurately and reliably measure a patient's bone density and to correlate the results of historical and future similar measurements on the same patient to monitor the bone density of the same patient.
In addition, there is a need for a BMD measurement system that is capable of housing a database with search and report generation capability that can archive all patient scan information.
These requirements indicate a need to both be able to repeat the measurement reliably on the same patient at different times and to make the measurements on many different patients in a consistent manner.
Consequently there is need for a BMD measurement apparatus and method that provides accurate reading and entails a short patient observation time, offers minimal X-ray exposure to the patient and minimizes a need for repositioning the patient.
In addition, a region of interest (ROI) is required to be defined in the patient's bones in trabecular bone rich areas, such that the ROI is consistently locatable at each patient measurement event.
Thus, there is also a need for a BMD measurement apparatus and method that provides high resolution images by using detectors having small lateral dimensions spaced closely together which images finer details of the bone and provides sharper edges for accurate, automatic and repeatable determination of the Region of Interest. Also, since the detectors are directly exposed to radiation during each patient scan, the detectors are susceptible to radiation damage. Hence, there is also a need to include in the apparatus, small sized detectors that provide reduced susceptibility to radiation damage and hence more consistent results over time.